The Nutrient Value of Straw
Cristie Preston, Ph.D.
Agriculture has always been an integral part of Dr. Cristie Preston’s life. She grew up in southwest Virginia and had interest in crop and animal agriculture since an early age. Once she began college, she initially chose to study animal science but switched to soil science. Dr. Preston attributes her decision partly to an influential professor who told her, “You can’t understand animals until you understand what they eat.” She received a Bachelor of Science degree in animal science and a Master of Science degree in crop and soil environmental science from Virginia Tech. Dr. Preston holds a Ph.D. in agronomy, focusing on soil fertility from Kansas State University. While completing her advanced degrees, Dr. Preston conducted more than six years of field and lab research. Dr. Preston has experience in laboratory research measuring volatility loss from urea-based fertilizers. Her field research has focused on phosphorus availability and the interactions with tillage and placement. She also has extensive experience in working with large data sets and analysis. Her main priority is helping growers to identify yield-limiting factors and fix those issues as cost efficiently as possible.
After wheat grain harvest this year, did you harvest the straw as well? Straw is an excellent carbon source for increasing soil organic matter, but it is also valuable as bedding or mulch. Straw does contain a significant amount of nutrients, so harvesting it does come at a cost.
Research at Virginia Tech shows the greatest amounts of nutrients removed were nitrogen at roughly 16 pounds per ton and potassium at 27 pounds per ton.
Researchers stress that “knowing your straw yield is imperative to correctly calculating your nutrient removal and may vary significantly with each field, with variety, and with year”. One method is to calculate your straw yield based on grain yield:
- Straw yield (pounds per acre) = (bushel per acre) x (60 pounds per bushel) x 0.80
First, you convert your yield from bushel per acre to pounds per acre by multiplying by 60 (1 bushel of wheat is 60 pounds). Then, straw yield is estimated to be 80 percent of the grain yield, so multiply by 0.80 to get your straw yield (in pounds per acre).
Furthermore, divide your straw yield (pounds per acre) by 2,000 to get yield in tons per acre. You can figure out nutrient removal rates by multiplying straw yield by 16, 2, and 27 to get the pounds of nitrogen, phosphorus, and potassium removed, respectively.